Computer hard disk drives, also known as fixed disk drives or hard drives, have become a de facto standard data storage component of modern computer systems and are making further inroads into modern consumer electronics as well. Their proliferation can be directly attributed to their low cost, high storage capacity and high reliability, in addition to wide availability, low power consumption, high data transfer speeds and decreasing physical size.
These disk drives typically consist of one or more rotating magnetic platters encased within an environmentally controlled housing that further includes all of the electronics and mechanics to read and write data and interface with other devices. Read/write heads are positioned above each of the platters, and typically on each face, to record and read data. The electronics of a hard disk drive are coupled with these read/write heads and include numerous components to control the position of the heads and generate or sense the electromagnetic fields representing data. These components receive data from a host device, such as a personal computer, and translate that data into magnetic encodings written onto the disk platters by the heads. Further, when a host device requests data from the drive, the electronics locate the desired data, sense the magnetic encodings which represent that data and translate those encodings back into the binary digital information which the host device can understand. Further, error detection and correction algorithms are applied to ensure accurate storage and retrieval of data.
One area in which significant advancements have been made has been in the area of read/write head technology and the methods of interpreting the magnetic fluctuations sensed by these heads. The read/write head, of which a typical hard disk has several, is the interface between magnetic platters and the disk drive electronics. The read/write head actually reads and writes the magnetically encoded data as areas of magnetic flux on the platters. Data, consisting of binary 1""s and 0""s, are encoded by sequences of the presence or absence of flux reversals recorded or detected by the read/write head. A flux reversal is a change in the magnetic flux in two contiguous areas of the disk platter. Traditional hard drives read data off the platters by detecting the voltage peak imparted in the read/write head when a flux reversal passes underneath the read/write head as the platters rotate. This is known as xe2x80x9cpeak detection.xe2x80x9d However, increasing storage densities require reduced peak amplitudes and better signal discrimination and higher platter rotational speeds are pushing the peaks closer together thus making peak detection more difficult to accomplish.
Magneto-resistive (xe2x80x9cMRxe2x80x9d) read/write heads have been developed with increased sensitivity to sense smaller amplitude magnetic signals and with increased signal discrimination to address some of the problems with increasing storage densities. In addition, another technology, known as Partial Response Maximum Likelihood (xe2x80x9cPRMLxe2x80x9d), has been developed to further address the problems with peak detection as densities and rotational speeds increase. Borrowed from communications technology, PRML is an algorithm implemented in the disk drive electronics to interpret the magnetic signals sensed by the read/write heads. PRML-based disk drives read the analog waveforms generated by the magnetic flux reversals stored on the disk. However, instead of looking for peak values to indicate flux reversals, PRML-based drives digitally sample this analog waveform (the xe2x80x9cPartial Responsexe2x80x9d) and use advanced signal processing technologies to determine the bit pattern represented by that wave form (the xe2x80x9cMaximum Likelihoodxe2x80x9d). This technology, in conjunction magneto-resistive (xe2x80x9cMRxe2x80x9d) heads, have permitted manufacturers to further increase data storage densities. PRML technology further tolerates more noise in the sensed magnetic signals permitting the use of lower quality platters and read/write heads which increases manufacturing yields and lowers costs.
With many different drives available from multiple manufacturers, hard disk drives are typically differentiated by factors such as cost/megabyte of storage, data transfer rate, power requirements and form factor (physical dimensions) with the bulk of competition based on cost. With most competition between hard disk drive manufacturers coming in the area of cost, there is a need for enhanced hard disk drive components which prove cost effective in increasing supplies and driving down manufacturing costs all while increasing storage capacity, operating speed, reliability and power efficiency.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. By way of introduction, the preferred embodiments described below relate to a method for fabricating a Viterbi detector having a predetermined number of states, wherein the Viterbi detector stores a state metric value and a branch metric value for each state, and wherein the Viterbi detector implements a trellis diagram. The method includes constructing a Viterbi detector which can support a state metric value having g+hxe2x80x2 number of bits. The number of bits needed to represent the branch metric value is represented by (g) and the additional number of bits needed to represent the state metric value is represented by (hxe2x80x2). The additional number of bits (hxe2x80x2) is less than the additional number of bits (h) determined using the following inequality: 2hxe2x88x921xe2x88x92hxe2x89xa7Kxe2x88x921 , wherein K represent the constraint length of the trellis diagram.
The preferred embodiments further relate to a Viterbi detector having a predetermined number of states for conducting maximum likelihood sequence estimation for a predetermined stream of binary data, wherein the Viterbi detector stores a state metric value and a branch metric value for each state, and wherein the Viterbi detector implements a trellis diagram. The Viterbi detector includes a branch metric unit which receives the stream of binary data, determines a branch metric value for each state at a time k+1, and outputs the branch metric value for time k+1. The Viterbi detector also includes an adding unit which receives the branch metric value for time k+1 and adds the branch metric value to a state metric value for time k for each state. The state metric value is represented by a number of bits (g+hxe2x80x2), wherein g is the number of bits needed to represent the branch metric value, and wherein hxe2x80x2 is the additional number of bits needed to represent the state metric value. The additional number of bits (hxe2x80x2) is less than the additional number of bits (h) determined using the following inequality: 2hxe2x88x921xe2x88x92hxe2x89xa7Kxe2x88x921, wherein K represents the constraint length of the trellis diagram. Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments.